This project intends to study the issue of regression in children who develop autism by examining early videotapes of 100 preschoolers with autism, compared to early videotapes of normal developing children. A comparison group without autism but with low IQ is also involved. Younger siblings of the children with autism form a fourth subject group. The researchers plan to classify the children with autism into one of three "onset" groups based on videotapes taken during the children's infancy; the three groups involved are: no regression, language regression only, and full autistic regression, which will include signs of regression in social and communicative areas.